I build my first F1J model in 2000 year. On photo below you can see my typical model with curved tips.

(Click on image to see enlarge photo)

Sketch of this model .

Cyclon and Fora 1cc engine can used on this model. 

Few photos of my models.

From 2015 I begin to use "Sidus" F1C electronic timer in my F1J/P models. It can be install for any previous F1J/P model. It does not need serious modification of the model.

More detailed photo "Sidus" on F1J model here sergf1.io.ua